1. Technical Field
The present invention belongs to the technical field of integrated semiconductor circuits, and relates to a method for improving the electromigration resistance in the Copper interconnection process.
2. Description of Related Art
With the continuous size reduction of semiconductor devices and the continuous enlargement of the chip area, people are faced with the problem of how to solve the remarkably increased delay of the RC (R stands for resistance and C for capacitance) caused by the rapid growth of the wiring length, which has been a critical constraint on the development of the semiconductor industry. To reduce the RC delay caused by the interconnection, a lot of measures have been taken.
Compared with conventional aluminum, copper has the following advantages: firstly, copper has a smaller resistivity (Cu: 1.7μΩ/cm, Al: 3μΩ/cm). Secondly, Cu interconnects have smaller parasitic capacitance than Al interconnects. Because of Cu's smaller resistivity and better conductivity, when both copper and aluminum withstand the same current, Cu interconnects have smaller cross sectional area than the Al interconnects, so the parasitic capacitance among adjoining conducting wires is smaller. Therefore, the signal interference is smaller. Since the time parameter RC of Cu interconnects are smaller than that of Al interconnects, signals on Cu interconnects transmit faster than that on Al interconnects, which benefits the high-speed UC. Thirdly, the smaller resistance of the Cu interconnects leads to smaller power consumption than that of Al interconnects. Fourthly, the electromobility resistance of copper is better than that of Al (Cu<107 A/cm2, Al<106 A/cm2), so no interconnect voids caused by electromigration will be produced, which improves the reliability of devices. As a result, it is more reliable for devices to use Cu as the interconnect metal. At present, the best integrated circuit interconnect system is the Cu/low-k dielectric interconnect system which, compared with conventional interconnect systems, has more advantages, such as less layers of metal interconnects, higher speed of chips, lower power consumption, lower cost and higher electromigration resistance.
However, with the continuous size reduction of semiconductor devices, Cu/low-k dielectric interconnect systems have more requirements for copper's electromigration resistance. Preparing a silicide coating layer on Cu interconnects is an effective method to solve the problem of anti-electromobility, but under high temperature, the extremely high diffusion coefficient of silicon in copper will lead to a large increase in the resistance of interconnects, which makes the right choice of coating layers and the development of a proper interconnection process a problem in bad need of a solution.